The present invention relates to personal computer (PC) card radio modems. Small hand-held personal computing devices can use Personal Computer Memory Card Interface Association (PCMCIA) radio modems to connect to a wireless network. PC card radio modems typically use battery power from the hand-held PC or from a battery pack extension.
A problem that exists in prior-art systems in which the wireless modem operates on a network such as the North American AMPS or CDPD network, is a battery pack extension is used to supplement the power supplied to the wireless modem. Typically, hand-held PCs use two AA batteries, which suffer from low capacity and a low peak current capability.
Six different standard RF power levels are required by the CDPD standard (CDPD R1.1 Part 409) and the AMPS standard (IS-19B) for a class III cellular device. With two AA batteries supplying the hand-held PC and the PCMCIA wireless card, it is difficult to achieve the highest RF power level; which, for a class III cellular device, is an output power of 28 dBm where 0 dBm is 1 mW output power. Typically, prior art uses a battery pack extension on the PCMCIA card to achieve the highest RF power output. This is an undesirable solution as the esthetics of the complete product are poor.
It is desirable to have an improved system, which avoids some of the problems of the prior art.
In one embodiment, the present invention relates to a PC card radio transceiver which uses a non-standard power output level. The non-standard power output level is limited by the peak sustainable current available from the battery inside the hand-held PC. In one embodiment, this current is limited to 600 mA. The non-standard RF power obtainable, given a 600 mA maximum limit, is typically between 24 dBm and 28 dBm (in one implementation, 26.5 dBm). The non-standard power output level has a nominal value less than the nominal value required by the standard, yet is still within the acceptable range (+2, xe2x88x924 dB) specified in the standard.
The advantage of the present invention is that the radio transceiver in the PC card can operate while attached to a hand-held PC without requiring a battery pack extension. The system allows the two AA batteries of the hand-held PC to produce an acceptable, high-level RF output power.
Implementation of a non-standard RF power level, which is based on a current restriction, requires the automatic leveling circuit (ALC) of the power amplifier to be a current leveling circuit as opposed to a power leveling circuit as in prior art systems. A current leveling circuit achieves the same effect as a power leveling circuit, given the load on the power amplifier remains constant. In practice, this is a reasonable assumption.